New model upload format

[mharvan]

In late July 2020, the AWS DeepRacer changed the requirements on the format of uploaded models. The model format is described at
https://docs.aws.amazon.com/deepracer/latest/developerguide/deepracer-troubleshooting-service-migration-errors.html

The current best way for local training seems to be:

1. Upload model to s3
2. Import model from s3 in AWS DeepRacer console.

Models uploaded with the script upload-current.sh fail to import with the new DeepRacer model service.